Engine cylinder fin and baffle construction



June 29, 1948. A P 01 BURN W 2,444,220

ENGINE CYLINDER FIN AND BAFFLE CONSTRUCTION Filed se it. so, 1944 4 1 a INVENTOR Allan R Co/burn ATTORNEY.

Patented June 29, 1948 ENGINE CYLINDER FIN AND BAFFLE CONSTRUCTION Allan P. Colburn, Newark, DeL, assignor to United Aircraft Corporation, East Hartford, Conn., a

corporation of Delaware Application September 30, 1944, Serial No. 556,561

1 2 Claims.

1 This invention relates to a heat exchange structure and particularly to a heat radiating structure and enclosing baffle for cooling aircraft engine cylinders.

A primary object of the invention is to provide an improved metal fin and baffle construction that will enable a cylinder, or other member, to be cooled uniformly circumferentially and which will have maximum cooling efiect over the entire surface of the cylinder barrel or other member with minimum air drag.

Another object of the invention is to improve the cooling effect of a fin and bafile construction surrounding a cylinder in which the baffle has a single opening for admitting air to the interfin spaces and preferably has groups of separate exit openings alternately'circumferentially spaced for individual or for several adjacent interfin spaces.

A still further object of the invention is to provide an air-cooled engine cylinder having intermediatecut-away fins alternating with complete annular fins, in which the alternate intermediate fins have their cut-away portions displaced circumferentially.

Another object is to arrange alternating, complete and cut-away fins within a baffle having circumferentially displaced exhaust openings in a manner to equalize the flow velocity or frictional resistance within the interfin spaces served by a single exhaust opening so that the longer path about the cylinder for air passing between adjacent complete annular fins may have the same air resistance as the shorter path about the cylinder, substantially all of the cut-away portions of the intermediate fins being disposed within the longer air passages.

Another object of importance is to increase the fin area surrounding the trailing half of the cylinder, the full diameter portions of the cut-away fins being disposed to surround the trailing portions of the cylinder while their cut-away portions are disposed to surround the leading half of the cylinder, also with the increased fin area in the trailing half, the velocity of the air mass within the trailing half is increased.

This application is a companion case to the application of Donald S. Hersey U. S. applica ion Serial No. 556,563, filed September 30, 1944, now abandoned, for Engine cylinder baffle, and represents an improvement and development thereon.

Other objects and advantages will be apparent from the specification and claims and from the drawing which illustrates what is now considered to be a preferred embodimentof the invention.

In the drawing, Fig. 1 is a front elevation of a portion of a cylinder provided with the baffle and fin structure forming the present invention.

Fig. 2 is a rear elevation of the portion of the cylinder and cooling structure shown in Fig. 1.

Fig. 3 is a plan view of the parts shown in Fig. 1.

Fig. 4 is a central longitudinal section of the cylinder and cooling structure taken on the plane of line 4-4 in Fig. 3.

Fig. 5 is a plan view of one of the intermediate partially cut-away annular fins, and

Fig. 6 is a horizontal sectional view taken on the plane of line 5-6 in Fig. 1, and showing one of the partially cut-away fins in position within the baflie.

In its preferred form, the invention may include the following principal parts: First, 2. cylinder barrel or other member having relatively widely spaced annular fins thermally united to the external surface of the cylinder walls; second, a battle partially surrounding and enclosing these fins and preferably being thermally united thereto; third, separate alternately circumferentially spaced exhaust openings formed in the baffle for exhausting air from spaces between one or more adjacent annular fins; and fourth, intermediate fins thermally united to the cylinder and having their outer periphery partially cut away, these fins being interposed between adjacent complete annular-fins, the cut-away fins being disposed with their cut-away portions alternately circum ferentially spaced, and also so disposed that there is a maximum fin area in the trailing portions of the cylinder.

In cylinder cooling in which annular circumferential radially extending fins are employed, it is desirable to make equally efiicient use of all portions of the surfaces of the fins to substantially equally cool cir-cumferentially all portions of the cylinder barrel. The front halves of the fins and cylinder are subject to air approaching the cylinder and accordingly are cooled to a maximum degree. The trailing halves of the cylinder and fins, however, must have the air constrained to contact them so that the greatest possible mass flow of cooling air will contact the maximum area of their surfaces. For this purpose an enclosing baiile is placed about the cylinder, there being a single large opening for the admission of air on the leading side of the cylinder. At the rear of the cylinder there preferably are provided separated circumferentially elongated exhaust openings formed in the baffle, each opening having a. vertical height or axial width equal,

in the embodiment of the invention illustrated in the drawing, to but two of the individual spaces between adjacent fins.

The exhaust openings in the baffle are alternately spaced circumferentially of the cylinder for spaces between adjacent complete annular fins. The cooling air, therefore, passing around the trailing half; of the; cylinder: is maintained in contact with the surfaces of the fins by the enclosing bafiie. A portion of the air passing through an interfin space is exhausted after pass ing a short distance circumferentially beyond the rear central portion of the cylinder. To further increase the efiiciency of the cooling fins, intermediate partially cut-away -finsz are interposed midway within the spaces between adjacent complete annular fins served by a single exhaust opening.

Paths for the cooling air entering the interfin spaces served by a single exhaust openingare unequal in length depending upon the direction taken by the'air in passing around the'cylinder to the exit openings. Means, therefore, are providedt'o equalize the frictional resistance within these paths of unequal-length so that substantially equal massfiowsof, airwill occur in each path. For this purpose the interposed cut-away fins have their cut-away portions extending principally within the longer path, the portion of the interposed cut-away finiof full' width extending substantially throughout the entirerlength' of the shorter path. 'Thelonger path','within which the cut-away portion is disposed, therefore, has more free air space than the shorter path, this greater free air space in the longer path serving to equalize the mass flow through the-two paths.

Also,- in order that the; maximum" cooling area may be available over the trailing half of the cylinder, the. full diameter portions of the cutaway fins: are disposedxso that they ext-end across the trailing'half.

Referring more'indetailto the figures of the drawing, I provide a'cylindert it, only a portion of which is shown in thedrawing, with a plurality of circumferentiazlly disposed radially extending fins'alternately'oftwo diiferent types I l and i2 extending'radially outward from the outer wall of the cylinder'and thermally'united thereto in any preferred manner. Fins of type H are of uniform width throughout their entire circum ference. Fins of typed? are annular also but have a part of their outer peripheries cut away as shown in Fig. 5." Both types of fins are of metal, having high heat conducting qualities, preferably copper or aluminum.

Partially surrounding and enclosing cylinder Hi and fins H and i2 is a thin cylindrical bailie member [3 preferably thermally united to the outer. edges of the fins. The front opening i l of the baffle l3 for admitting air to the-interfin spaces within the bafile i3 is relatively wide and preferably extends the full length of the portion of the cylinder ill being cooled. In the trailing portion of the cylinder it are provided narrow circumferentially elongated slots oropenings id in the baffle l3 forming exhaustopenings for the air within separated interfin spaces. Exit openings in the embodiment of the invention selected for illustration are spaced apart circumferentially of the cylinder It on either side of the central portion so that they are arranged in two circumferentially spaced groups. The openings [5 of. each group are disposed in axial alignment.

. Disposed centrally'withinthe space between adjacent complet'e circumferential-or" annular II are fins of type l2 similar to that shown in Fig. 5 in which a large arcuate portion of the outer periphery has been cut away. These partially cut-away fins i2 are spaced midway between adjacent full annular fins H. Preferably, and as shown, the spaces between these full annular fins II on either side of a cut-away fin l2 are served by a single exhaust slot or opening l5.

It will be noted from the above that air, entering the individual spaces between adjacent full circumferential fins l I on either side of an intermediate partially cut-away fin i2, may pass around the cylinder 83 in either direction to an exit opening l5. In passing around the cylinder inone direction, the cooling air will have a much shorter path to' theparticular exhaust opening i5 for that section of the cylinder ill than air passing around the cylinder in the opposite direction. This will be seen by an inspection of Fig. 6. In order to maintain equal frictional resistances in the two paths so that substantially equal air masseswill flow in each direction, the partially cut-awayintermediate fins it have substantially all of their cut-away portions disposed within the longer paths. There is, therefore, more free space-for the cooling airwithinthese longer paths. In the shorter paths, however, where the interm-ediatefins have their full width, theair has to pass within the restricted spaces on either side of the intermediatefin. The cooling air, therefore, in passing around the-cylinder H] through the longer path, will have a relatively free path for a major portion of its length-and the air passing around the cylinder through the Ishorter path will have a morerestricted path.

Substantially equal'mass flows-of air will, therefore, occur in each path and the radiating surfaces in the two pathstherefore, will be substantially'equally eifective. Also as aportion of the cooling air passing around the trailing half of the cylinder lil'has to pass beyond the center of this half of the cylinder wall, thefinarea adjacent this mid-portion. of the trailing half of the cylinder ill will be most eifectively utilized.

Some of the advantages of'using: cut-away fins, as disclosed in this application, either with the exit openings IE or with a single large exit opening corresponding to the inlet opening it, are as follows: First, they provide more finned surface area in rear than in front; second, they reduce the resistance ,to' the fiow of cooling air; third, they decrease the weight of cylinder construction; fourth, they change the relative airflow resistance on opposite sides of the cylinder and ;cause th airstream" on the side with the greater mass flow to flow across the rear of the cylinder and, thereby, effectively cool this portion of the cylinder. This effect of causing air to flow past the center of the trailing half of the cylinder is made to alternate from side to side by. the provision ofthe two groups of .circumferentially spaced exit openings I5.

. In. addition to-incr.easing the airflow rate across the rear of the.cylindenbecausemore air. has come through the wider flow path, the trailing portion is more"eifectively cooled. Also there is a higher air velocity acrosst'he trailing half of the cylinder andfor'this' reason" the air contacting this trailing 'half 'of the cylinder is cooler.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from the spirit: of the invention 'defined by :the following claims.

I claim:

1. A cooling structure for cylinders comprising in combination, a cylinder barrel, a plurality of spaced annular fins surrounding said barrel, alternate fins having cut-away portions, said cutaway portions being spaced circumferentially of said barrel, and a ba-fiie partially enclosing said barrel and fins and having circumferentially spaced exit openings for pairs of interfin spaces, said openings forming a longer and a shorter circumferential airflow path in each interfin space, and said cut-away portions of said fins being disposed in the longer path substantially to equalize airflow therein.

2. A cooling structure for cylinders comprising in combination, a cylinder barrel, a plurality of spaced annular fins surrounding said barrel, alternate fins having cut-away portions, said cut away portions alternately spaced circumferentially of said barrel, and a bafile having a central front opening and partially enclosing said barrel 20 and fins and having alternately circumferentially spaced exit openings for adj acent; groups of interfin spaces, and forming a longer and a shorter circumferential airflow path in each interfin space, and said cut-away portions of said fins being disposed in the longer path substantially 5 to equalize airflow therein.

ALLAN P. COLBURN.

REFERENCES CITED The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS Number Name Date 1,966,785 Boucher, Jr. July 17, 1934 15 1,997,502 Van Seld et a1 Apr. 9, 1935 2,031,891 Irgens Feb. 25, 1936 2,330,065 Lucke Sept. 21, 1943 2,422,936 Sweger June 24, 1947 FOREIGN PATENTS Number Country Date 110,125 Great Britain Oct. 11, 1917 France Jan. 11, 1936 

